The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1887-12-31
THE LOGIC OF THE TIDES.
Rising so Feet in the Bay of Fundy,
and Feet at New York.


and 5 Feet at New York.
A correspondent, who signs his letter with
the initials L. B. g., asks the New York
Sun number of questions about the inter-
esting subject of the tides. Among other
things he wants to know what causes the
tides, and whether tidal wave enters
the eastern end of Long Island Sound and
another at the Narrows at the same time,
and, if so, where the two waves meet. lie
has noticed that on certain date high tide
at Sandy Hook occurred in the afternoon
twenty-three minutes more than twelve
hours after it occurred in the forenoon,
while at He'll Gate the evening tide was
twelve hours and thirty-four minutes after
the morning one, showing that the tide was
retarded eleven minutes more at Hell Gate
than at Sandy Hook. He wants to know
WHY this was so. He has heard that the
difference between high and low water at
ST. John, n. B., or that the rise of the tide
at that place is thirty feet, while in New
York it is only from four to five feet, and
he wants to know why that is so.
The rise and fall of the tide, that is, the
elevation aud depression of the surface of
the water of the ocean, and the bays and
tributaries that empty into are due in gen
eral to the attraction of the sun and moon on
the earth. The surface of the earth that is
nearest to the sun and moon, when the two
are in line on one side of the earth, is at
tracted more strongly toward those bodies
than the centre of the earth is, because the
isurface is nearer to them than the centre
s; the centre is attracted toward them more
strongly than the further surface Of the
earth is for the same reason. These great
heavenly bodies are constantly Pulling the
earth toward them, and the particles of
water in the sea on the side nearest are af-
fected so much by this influence that they
are heaped up as if endeavoring to fly off
toward the power that is pulling them.
But the centre of the earth being attracted
more strongly than the further surface, the
water on the further surface is heaped up
because the earth falls away from it as it
drops from the straight line of "a tangent
through the curve that it follows. The
water on the further side Of the earth comes
dragging on behind, much as a whip-lash
follows the whip-stalk that is waved through
the air, while the water on the near side of
the earth is heaped up as iron filings heap
up oil a table when placed beneath a pow
erful magnet Thus it happens that We
have two tides in day. One is the heap
of water drawn up by the direct attraction
of the sun and moon on it; the other that
follows little over twelve hours later is
the heap or wave that is piled up because
the earth drops away from it.
It regularly happens every month that
the moon is on one side of the earth pulling
the water in its direction, while the sun is
on the opposite side pulling the water to-
ward it, instead of both being on one side
The effect of this is much the same on the
water as when both are ON one side. 1t is
on such dates as these-namely, when
there has been a new moon and when there
has been full moon-that the tides rise
highest the moon and the sun both work
together then in heaping up the water.
But at the first and third quarters of the
moon the sun and tn moon work against each
other. The heap of water that the sun is
pulling along after it as it apparently tray
els around the earth comes into port just
as the moon is trying to drain the port by
pulling all the water toward its location
one-half the way around to the opposite
side of the earth. The consequence is
that the suns heap of water partly fills up
the depression caused by the moon. Where
the moon is heaping up the water the sun
is drawing it away, and the consequence is
that the tide levels are neither so high nor
so low at such times in the month as they
are when the two great luminaries work
together The high tides of the new and
the full of the moon are known as spring
tides; the low tides of the first and third
quarters are called heap tides. The moon,
it is observed, always gets the best of the
sun when the two are not working together.
This is due to the nearness of the moon to
the earth. Although the sun is many
times larger than the moon, the moon ex-
erts more than twice as much power on the
water. But this power is modified in va
rious ways. The sun may be on one side
of the equator and the moon on the other,
and both on one side of the earth. They
would not then pull together quite as well
as when both were on one side ofthe equator
and in right line. The earth may be
very near to the sun, as it is in january
which would increase the relative influence
of the sun, or it may be far away, as it is in
june, when the moon is relatively more
powerful Then the moon varies in its
distance from the earth, too, and this tends
to complicate matters.
Then there are infuences local to various
parts of the earth that vary the rise and
fall of the tides. Thus, if for couple Of
days or so when The spring tides are on us,
there should prevail a strong southeast wind
the water in New York would be heaped
up so that ferry passengers would feel as il
they were climbing stairways when they
went up the bridges to the boats, while all
the rats along South and West streets would
get drowned out
New York itself is pretty well situated
for high tide, but not so well as Boston,
and not nearly so well as St. John, N. B.,
although the rise Of the tide at St. John is
but nineteen feet instead Of thirty, as the
correspondent has been told. If any one
viii look at map of North America he
will see that from Florida to Cape Hatteras
the lard sweeps in forming very long
shallow bay, with Savannah about at the
head Of the bay. North of this there j.
another bay, of which Hatteras may b.
called one headland and Nantucket Islanc
another. New York is IN the blight, or al
the head of this bay. Now, the tide at the
lower end Of Florida rises less than two
feet, but at Savannah it rises seven and o